Insulating structure



Feb. 6, 1968 H. T. DARLINGTON 3,367,527

INSULATING STRUCTURE Filed May 1, 1967 JNVENTOR. HAROLD T. DARLINGTON ATTORNEYS United States PatentOfice 3,367,527 Patented Feb. 6, 1968 3,367,527 INSULATING STRUCTURE Harold T. Darlington, 1175 York Ave., New York, N.Y. 10021 Continuation-impart of application Ser. No. 535,846, Mar. 21, 1966. This application May 1, 1967, Ser. No. 634,956

Claims. (Cl. 2209) ABSTRACT OF THE DISCLOSURE An internally insulated receptacle for the confinement of cryogenic fluids is described, wherein insulating blocks are bound on one end to the metallic shell. When a cryogenic fluid is placed in the receptacle, the four sides of each of the insulating blocks become inwardly tapered in the direction of the cryogenic fiuid, and the fluid that flows into the recesses between the blocks vaporizes. To prevent this fluid from flowing into the recesses, an inner liner can be placed inside of the space formed by the mounted blocks.

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of my pending application Ser. No. 535,846, filed Mar. 21, 1966, now abandoned.

BACKGROUND OF THE INVENTION (1) Field of the invention My invention relates to internally insulated receptacles for the confinement of cryogenic fluids and, in particular, to receptacles wherein the contractional effect of the adjacent cryogenic fluids upon the insulation is distributed uniformly over a fixed predetermined location.

(2) Description 'of the prior nrt Gaseous derivatives produced during the refining process of crude oil generally are compressed to their liquid states in order to benefit from the greatly reduced volume inherent in the liquid state both in the transportation and storage of the derivatives. However, because the petroleum derivatives comprise such cold boiling gases as propane having an initial boiling temperature at 44 F. and methane having an initial boiling temperature at 259 F., extremely high pressures requiring massive structural facilities are necessitated for containing the liquefied petroleum derivatives unless refrigeration is utilized to reduce the required pressure. By lowering the temperature of the gaseous derivatives to their initial boiling point or lower, relatively lightweight structural metals can be utilized for construction of the receptacles designed for vapor pressures of up to about six pounds per square inch, thereby providing benefits both in the initial fabrication of all receptacles and in the subsequent transportation of those receptacles used in transporting cryogenic fluids. As petroleum producing areas are often quite distant from the point of consumption, lightweight facilities for the confinement of the liquefied gases provides considerable savings in transportation by, for example, ships, railway cars or trucks. Such lightweight receptacles must function under the same thermal conditions as the structurally massive facilities, and absorption of heat from the surrounding atmosphere must be either controlled or removed by refrigeration, unless the receptacle pressure buildup is vented to prevent the bursting of the receptacle.

In recent years attempts have been made to externally insulate metal storage tanks for liquefied petroleum gases by the utilization of low density materials such as cork, wood fibers, asbestos and various types of urethane foams. External insulation is unsatisfactory, especially when used in confined spaces such as on ships because in addition to the volume which it occupies, void spaces must be provided to permit inspection and repair. Further, the tendency of normal condensation and absorbed moisture to freeze destroys the insulation thus affecting the thermal resistance. Another difficulty in using such a system on ships is that of securing the externally insulated container to the hull and the related problem of relieving the strain produced by contraction of the metallic container when placed in contact with the cryogenic liquid.

In order to overcome the deficiencies inherent in externally insulated containers, attempts have been made to internally insulate cryogenic tanks by installing the insulating materials intermediate the liquefied gases and the metallic structure of the tank. These attempts have usually proven to be unsatisfactory because of confined moisture inherent within the insulating materials which subsequently freezes to destroy the integrity of the insulating material. The attempts have also been unsatisfactory because the insulating material has a shrinkage factor which, despite all attempts to anchor it, causes it to rupture, creating random fissures through which the cryogenic liquid penetrates towards the metallic shell and, by saturating the insulation, nullifies its value as a thermal barrier, thereby causing embrittlement of adjoining metallic supporting structures.

SUMMARY OF THE INVENTION My invention is accomplished by providing a plurality of moisture free insulating blocks fixedly secured to the internal surface of the metallic shell of a cryogenic container. The cross-sectional area of each block of the internal insulating lining is so dimensioned that a predetermined contraction is produced in any transverse dimension of the interior face of the insulating block by the reduced temperature of the adjacent cryogenic fluids with a synthetic rubber liner intermediate or when in direct contact with the cryogenic fluids. Because each block is secured in position only by the single face contacting the metaliic shell with all the insulating blocks lying in juxtaposition with adjoining faces abutting, the predetermined contractional variation of the face adjacent to the fluid with the liner intermediate or in direct contact with the fluid produces uniformly distributed fissures positioned intermediate the abutting faces of the insulating block, which fissures are sufficiently small to prevent extrusion of the synthetic rubber liner thereinto or in case of rupture, failure or complete absence of such a liner, are sufficiently small to convert any seepage of cryogenic fluids therein to a saturated vapor barrier. Generally, these fissures should be no greater than about 0.025 inch when a synthetic rubber liner is used intermediate the fluids and the insulation, an'd for greater protection in case of failure of the liner, or no liner, can be as small as about 0.010 inch, depending on the cryogenic liquid in the container. The dimension of the fissure, and the thickness of the insulation, should be designed to fit the coldest cryogenic fluid `for which the receptacle is intended, and in relation to mean and maximum ambient temperatures in which the receptacle is to operate. Similarly, and as a further safety precaution, the metallic shell should be of suitable material which will not become embrittled if exposed to the temperature of the cryogenic fluid for which it is designed. External stiffeners and external web frames required to stren-gthen the metallic receptaclel sufficiently to counter this hazard, by using web frames between the tank and the ground.

In case of failure of the synthetic rubber liner or the absence thereof, cryogenic uid will be forced into the fissures produced by the contraction of the insulating blocks lby hydrostatic head and surface vapor pressure of the cryogenic fluid contained in the receptacle. With few exceptions, the normal boiling point of liquefied gases is lower than ambient atmospheric temperature. Under these conditions, the cryogenic fiuid so forced into the fissures must absorb heat from the insulation and from the adjacent metal, and changes from a saturated liquid into a saturated gas, and it is not until the gas has absorbed enough heat to raise its vapor pressure above that of the hydrostatic and combined surface vapor pressures that the gas will vent from the fissures. Other than the pressure of the overlying liquid, there is no practical way of retaining these gases in the Hoor of the receptacle. However, despite vertical seams in the walls being offset in each course, there is a tendency for the gas to creep upwardly through the unsecured vertical and horizontal seams of insulating block, and to impede its progress, unitary layers of sheet material impervious to the gases are provided in the horizontal courses of block. Thus, at all levels in the kwall excepting the uppermost course and in the fioor, gases trapped in fissures are held in by the pressure which forced the fluid into the fissures. The gases vented from the vertical seams and the horizontal seam of the uppermost course, which is only partially covered by liquid, are not blocked. However, at this level, hydrostatic pressure is at its lowest, and gases so generated in a wax and wane cycle as each course becomes exposed are re-cooled with the gases formed by overall heat transfer `from the surrounding atmosphere through the insulated metallic receptacle. Re-cooling of vapors is standard procedure for many gases, although gases resulting from methane can be transmitted into distributory systems, and on ships may be used as boiler fuel.

The use of an inner liner of synthetic rubber is optional and depends upon the economics f its cost as compared to the cost of re-cooling vapors where required, which can be reduced by about fifty percent by use of such a liner. Where liquefied methane is transported by ship and any boil-off thereof is used in place of more conventional boiler fuels, a liner would probably be desirable because the methane is stored at ultra-low temperatures which makes it impractical to re-cool vapors on shipboard. The purpose of the liner is to prevent liquid from seeping into the fissures which develop through contraction of the insulating blocks. The inner liner can be made of any suitable material, besides synthetic rubber, which possesses the necessary properties which are apparent from the general discussion of my invention.

An inner liner, to fulfill the requirement of preventing cryogenic liquid from coming into contact with the insulation, must be completely free of the insulating blocks and in no way attached thereto. However, the liner must lie over the floor and -must cover the Walls, in juxtaposition to the insulation blocks in all receptacles, and when applied to receptacles used in transportation, especially on shipboard where vessel trim and motion may cause the cryogenic liquid to be in contact with the roof of the receptacle, the roof must also be covered without attaching the liner to the insulating blocks. The liner is hung from the upper periphery of the Walls only and, at suitable intervals, one-way valves are installed some two or three inches below the point of suspension to permit entrapped air or gas to be released. Similar one-way valves are installed in the roof cover of the liner when it is used.

Preferably, these synthetic rubbers are non-porous, are '0.063 inch thick, and weigh about eight ounces per square foot ofa sheet that thick. When properly formulated, the 'synthetic rubbers do not become brittle at the design temperatures. As the synthetic rubbers have a relatively high shrinkage factor of about 0.70 l04 inch/inch/ F they should be not be attached to the insulation. The liners for large receptacles must be built in place from rolls usually of 48 inches width, using an adhesive of the same basic material for lapped joints which are proven leak-proof by suitable tests, and are built to an oversize in each dimension, namely, about l percent for propane, about 21/2 percent for methane, etc. The surplusage is evenly distributed over all surfaces to minimize creep as it is brought from the manufacturing temperature of 65/ 70 F. to the operating temperature. This distribution should be verified immediately prior to filling the first cargo, when air is displaced from between the liner and the insulation. Thereafter, positive internal pressure is maintained on the receptacle at all times, and the liner will remain in place, even though it contains no cryogenic liquid, due to the one-Way valves.

Because the low density, moisture free insulating materials (having desirable thermal insulating characteristics for utilization in the cryogenic container of this invention) are characterized by a vulnerability to abrasion during both the construction and subsequent utilization of the container, `a protective shield, such as an organic plastic material, is employed to encapsulate each block of insulating material. Also, the encapsulation provides a means of obtaining a dimensionally uniform block which is important in the proper laying up of the blocks. Although care is to be exercised during the fabrication of the encapsulated blocks to completely enclose the insulated core, a rupture of the organic plastic shield is not catastrophic to the proper functioning of this invention, provided there is sufficient skin on the blocks to protect them from damage during installation or in case of subsequent cargo contact.

DESCRIPTION OF THE DRAWINGS A more complete understanding of the basic principles can be obtained from the appended drawings in which:

FIGURE 1 is an exposed schematic diagram of the cryogenic receptacle of this invention, viewed from above and to the right side of the receptacle, showing the optional inner liner;

FIGURE 2 is a sectional view of the encapsulated insulating blocks of this invention;

FIGURE 3 is a view taken along line 3 3 of FIG- URE 1 depicting the fissures between the insulating blocks in an exaggerated manner for purposes of illustration.

' FIGURE 4 is an interior elevation of a wall of the cryogenic receptacle of this invention before becoming adjacent to the liquefied cargo with a synthetic liner intermediate or in the absence or failure of such a liner, before contacting the liquefied cargo;

FIGURE 5 is an interior elevation of a wall of the cryogenic receptacle of this invention after contraction by the liquefied cargo with the fissures between the insulating blocks being depicted in an exaggerated manner for purposes of illustration; and

FIGURE 6 is similar to FIGURE 1 except that the View is taken directly into the exposed schematic portion of the receptacle.

DETAILED DESCRIPTION Referring to FIGURES l and 3, receptacle 10 for the retention of cryogenic fluid 12 generally includes metallic outer shell 14 interiorly lined by a plurality of encapsulated insulating blocks 16, face 46 of each of the blocks 16 is fixedly secured to the metallic shell 14 with face 48 opposite said secured face being adjacent to confined cryogenic fiuid 12 with synthetic rubber liner 70 inter mediate, or, in the absence or failure of liner 70, in direct contact with cryogenic fiuid 12. Receptacle 10 is constructed so that it has a removable top 90. Flanges 82 and 84 extend outward from receptacle 10 at the interface between top and the remainder of receptacle 10. Portions 78 and 80 of liner 70 are lapped into the interface between top 90 and the remainder of receptacle 10 and anges 82 and 84. Although receptacle 10 is depicted as being seated within the perforated support structure of a ships hull, the teachings of my invention are also applicable to other mobile installations, e.g., truck or railroad car tanks, as well as to xed installations. Cryogenic fluids 12 are admitted or exhausted through conduit 18 and orifice 20 positioned atop receptacle 10 by means of deep well pump 25 positioned on the bottom face or Hoor of receptacle 10 dependent upon the operational mode of well pump 25. The gaseous vapo-rs formed within receptacle 10 are expelled through conduit 26 and pressure valve 28 which communicate the interior of cryogenic receptacle 10 with exhaust 30. Any of the existing systems for liquefying, cooling and returning these vapors as cryogenic uid into receptacle 10 may be incorporated into the system if desired, or the vapors may be otherwise used or burnt off. Conduit 26 also functions in conjunction with valve 32 and carbon dioxide source 34 to maintain a constant positive pressure within receptacle 10 during the exhaust of cryogenic Huid 12 through conduit 18, thereby preventing the danger of explosion caused by seepage of air into the closed receptacle.

Referring more particularly to FIGURE 2, encapsulated insulating block 16 utilized to line internally cryogenic receptacle 10 is shown in section and generally includes a low density, moisture free core of insulating material 40 embedded within an external sheathing 42 comprised of a relatively tough organic plastic material to protect the core from physical damage during installation or subsequent contact with the liner 70 or cryogenic fluid 12.

Foamed volcanic glass, described in United States Patent No. 2,946,683, issued July 26, 1960, has been found to be particularly suitable for utilization as insulating core 40 because it is red at a temperature of 1500" F. during the manufacturing process, thereby producing a finished product which is completely moisture free. Other favorable thermal insulating ch-aracteristics of the foamed volcanic glass include a low expansion shrinkage factor of about 0.69 105 inch per inch per degree F. variation in temperature and a heat conductance factor which varies from about 0.43 at a mean temperature of F. to about 0,265 at a mean temperature of 200 F. per degree F. variation in temperature through one inch thickness. Other materials may be used provided they have sufficient structural strength and thermal insulating qualities, an have suitable expansion shrinkage factors.

The organic plastic material of sheathing 42 is preferably a polyurethane. Particularly suitable are the series of liquid urethane polymers (reaction products of a diisocyanate and a polyalkylene ether glycol) sold under the tradename Adiprene. These polymers, when cured, have high tensile strength and resilience, and have excellent resistance to abrasion, compression set, oils, solvents, oxidization, ozone and low temperature. The polymer sold as Adiprene L-l00 is particularly suitable. Sheathing 42 does not function as an insulator but rather serves to protect core 40 during the initial installation of insulating blocks 16 along the interior of receptacle 10 and the subsequent service life, and to provide a dimensionally uniform block for more precise installation. The polyurethane sheathingis extremely tough and, even at temperatures far colder than 260 F., has good elongation capabilities before rupture. So long as there is sufficient skin 42 on blocks 16 to protect them until they are installed (with a smooth coating on innermost face 48 which is adjacent to or in direct contact with the cargo), a rupture of skin 42 is not catastrophic, the reason being that a rupture in one block 16 would not affect any of the adjacent blocks 16 as they are not bonded to one another.

As cryogenic liquid 12 may reach metallic shell 14 in case of an accident, it is desirable to construct the shell of the receptacle containing the cryogenic material of a metal which does not become embrittled when lowered to the temperature of the cargo. Modified steel is suitable for liquefied gases at temperatures as low .as 50 F.,

6 but for temperature below 50 F., shell l14 should be constructed of either nickel steel or aluminum magnesium alloy.

As best shown in FIGURE 6, the vertical wall of inner liner 70 is hung from upper wall 72 of metallic outer shell 14 of receptacle 10 in all cases, and, vin the case of receptacles used for transportation, the section of the liner which covers the roof is also supported by brackets 74. To dissipate any undesirable pressure buildup between liner 70 and insulation blocks 16, one-way valves 76 are placed in the side surfaces within a couple of inches from the top, and also in the roof section where used. As mentioned before, liner 70 is an optional feature, the use of which may depend upon the various relative economic features also mentioned before. Internal pressure of liquid and/ or vapors causes the liner to overlie insulation blocks 16 at all points but it not attached thereto.

More specifically, my tests of receptacle 10 have produced certain phenomena, to wit: after the receptacle has been completed and insulation installed in accordance with the teachings of my invention, the insulation and the metallic shell retain heat obtained from the surrounding atmosphere and the sun. When liquefied gas 12 is introduced and reaches the iioor of receptacle 10, the heat entrained in the floor causes immediate ebullition, which continues violently until the oor is covered with liquid. Once the oor is covered with liquid, the ebullition subsides. Meanwhile, there is a continuing reduction in temperature of the metal to the point that dew forms on metallic shell 14. The test, made in still air and commencing in daylight, revealed that metal in the shade was at least 20 F. colder than metal in the sun, at all points. Between sunset and sunrise, always in still air, the difference became smaller until all sides were at the same temperature. The mean metal temperature was generally 5 to 10 F. colder than the surrounding atmospheric temperature. Tests were conducted without synthetic rubber liner 70 to determine' the effect on the metallic container as the cryogenic liquid entered fissures where vapors were not blocked. At this level, the metal temperature remained at the mean between atmospheric and that of the cryogenic fluid, causing ice from relative humidity. The width of the ice formation ranged from one-half of the height of a wall caurse to one and one-half times the height of the course (i.e., width of one block 16). Immediately above and immediately below this varying strip, the metal temperature was normal; as the receptacle was emptied, the ice strip melted on the upper edge, causing dew again which, as it iiowed downwards, added to the icing feature. Additionally, these tests were performed under the following conditions, to Wit: complete absence of synthetic rubber liner 70, and insulation thickness was designed 331/3 percent less than that required for ambient temperatures prevailing during the tests in order to exaggerate performance conditions and simplify observance.

These phenomena show that (a) when initially 'filling receptacle 10, and thereafter when refilling, cryogenic uid 12 should be introduced slowly until the iioor is brought into thermal equilibrium, and (b) the leeward and/or shady sides of tanks, especially if a liner fails, or in the absence thereof, are more likely to be partially exposed to the uids, indicating the desirability of sutable metals for the outer metallic shell.

The formation of ice on stationary storage tanks is desirable when the metallic shell is of suitable stock, and will reduce thermal conductivity. For example, in areas Where seasonal temperatures are high with relative humidity low, insulation thickness would have to be designed to offset the seasonal high temperature, whereas in a humid climate, the thickness could be designed to tit the mean temperature, with icing giving additional insulation. Obviously, when icing becomes severe, it should be washed away by hosing. This same principle maybe applied to insulated tanks used on trucks and railroads.

A different circumstance exists on board ships. Since ballast water may not be carried in the insulated tanks, provision must be made on board for ballasting in doublebottom and wing tanks, and perhaps in coffer-dams between insulated tanks for cryogenic cargoes. Upon arrival at a loading port, the ship will discharge ballast from on board. All such ballast tanks and void spaces should be fitted with pressure-vacuum relief valves of suitable range. Thus, when empty, these spaces will contain a certain amount of air. As loading takes place, the spaces will probably cool and humidity will precipitate. This can then be pumped out and the contained air, now dry, becomes dead. If necessary, it may be circulated through heat exchangers to keep the vessels structurals at safe temperatures in cases where thermal flow from the sea is inadequate. However, the same air remains in these void spaces during the loaded voyage, subject to minor breathing under the pressure-vacuum control, and the metallic container is not subjected to a iiow of new moisture-laden air. Once the cryogenic liquid has been evacuated from the multiple receptacles and ballast water is introduced into the void spaces, the metal surface exposed to the water immediately assumes the same temperature as the water. Since the receptacle now contains vapors only, thermal flow between the water and the gases is controlled by the conductivity of the insulation.

Most cryogenic liquids, being of low specific gravity, will seldom constitute a full load to a ships deadweight capacity. In this case, suitable make-up cargo may be carried in void spaces adjacent to the insulated cryogenic receptacles. Such make-up cargo, overlying the ships skin, would then conduct heat from structures exposed to the sea or atmosphere towards the metallic shell of the cryogenic tanks. This shell would then assume a facial temperature close to that of the sea or atmosphere, while the internal insulation would control the thermal flow. Under these circumstances, the insulating blocks would be designed with a facial dimension suitable to the temperature of the coldest cryogenic cargo to be carried and with a thickness dimension suitable to the highest seawater temperature anticipated.

In general, and for ship application, an inner liner of synthetic rubber is recommended. This would not only prevent the entry of cryogenic fluids into fissures, but further would permit the use of insulated receptacles on board ship for other non-volatile cargoes when desired, and subsequent cleaning of the tanks, and prevent retention of non-cryogenic fluids in fissures, which fluids might solidify or freeze in the fissures or contaminate cryogenic iiuids when the receptacle is returned to cryogenic use.

Thermal characteristics of the foamed glass are such that heat transfer from the outer metallic structure to the contained cryogenic iiuid follows a simple formula. Using 60 F. as the source of the thermal flow, a heat transfer of 5.85 to 6.00 B.t.u.s per square foot of surface per hour would require 71/2 inches thickness for propane and 18 inches thickness for methane. If the design heat source is below 60 F., insulation thickness must be reduced by 0.075 inch for each 1 F. below 60 F.; if the design heat source is above 60 F., insulation thickness -must be increased by 0.075 inch for each l F. above 60 F. to maintain this same thermal transfer. Thereafter, by reducing or increasing insulation thickness, thermal transfer will be increased or reduced, e.g., 50 percent reduction of thickness increases thermal transfer by 100 percent, while a 100 percent increase of thickness reduces thermal transfer by SO-percent on the basic formula in each case.

. In designing insulating blocks 16, it is necessary to make provision for the natural shrinkage of insulating core material 40 produced by the temperature variation between its outermost face 46 in contact with metallic shell 14 and its innermost face 48 lying in proximity or in contact with cryogenic fluid 12, which creates a plurality of fissures 50 between insulating blocks as shown in exaggerated form in FIGURE 3. Because there is a heat input through metallic shell 14 and insulating blocks 16,

a fixed rate of boil-off of cryogenic fiuid 12 is produced, dependent on the thickness of the insulating blocks intermediate the cryogenic fluid and the metallic shell, and innermost face 48 is at the initial boiling temperature of cryogenic uid 12. In case of failure of synthetic rubber liner 70, or in the absence thereof, that portion of cryogenic fiuid 12 tending to flow within fissures 50 towards metallic shell 14 is converted to a saturated vapor by the temperature differential along the length of insulating blocks 16 to block outward flow of the cryogenic liquid cargo. Obviously, if apertures 50 are sufficiently large, cryogenic liquid 12 would fiow into fissures 50 unobstructed by the partial vaporization of the fluid to embrittle support structure 15, and therefore it is necessary to prevent massive shrinkage of innermost faces 48 of insulating blocks 16 which would give rise to major crevices therebetween. Careful research has shown that liquefied gas at its initial boiling point will not easily enter a fissure as m-uch as about 0.063 inch wide so long as there is a heat sump causing vaporization. The basis of my invention lies in evenly distributing the shrinkage of the innermost face 48 into as small segments as possible, consistent with economy, to prevent its lbuildup in one section.

For example, assuming it is necesary to construct receptacle 12 for liquid propane having a temperature of 44 F. within a climatic environment of F., if fused volcanic glass insulating blocks 16 having a 12-inch by l2- inch cross-section are utilized, innermost face 48 is reduced in length in each traverse direction by an amount equal to the temperature variation (124 F.) times the shrinkage factor of the volcanic glass (0.69X10r5). The 12-inch traverse dimension will contract to 11.990 inches, thereby creating fissures of '10.0 mils between adjoining innermost faces 48. If the metallic shell temperature were required to be at or slightly above 32 F. to prevent formation of ice externally thereupon, outermost faces 46 would shrink 4.0 mils as calculated from the temperature variation of 48 F. times the shrinkage factor of vol-canic glass. If metal shell 14 is fabricated from steel, it will shrink almost identically with outermost face 46, thereby effectively closing the crevice between the outermost faces. Fissue 50 will therefore assume a Vgenerally triangular configuration having a base of approximately 6.0 mils located between innermost faces 48. If external icing is permitted involving temperatures lower than 32 F., the contraction of metalli-c shell 14 and blocks 16 being almost identical, will further reduce the base of the fissure. Further, by using smaller cross-sections, the crevice is further reduced, e.g., with a cross-section of 6 inches by 6 inches, facial fissures of 5.0 mils would result, with the triangular configuration having a base of 3.0 mils on metallic shell 14 at 32 F. However, since metallic shell 14 is the first to be exposed to the thermal source, the shell temperature will not remain constant nor will that of the block fa-ce attached to the shell, in view of changing atmospheric conditions, solar radiation, or on ships, even seawater temperatures.

Assuming a receptacle were designed for a mean ambient temperature of 60 F. and at this temperature a maximum thermal inflow of 6.0 B.t.u.s were to be obtained, the thickness of the insulation would be designed at 7.500 inches. Thus, thermal transfer expressed in B.t.u.s per square foot per hour would be 3.46 when the outer metal was at 20 F., 4.62 B.t.u.s per square foot per hour at 40 F., 5.85 B.t.u.s per square lfoot per hour at 60 F., 7.05 B.t.u.s per square foot per hour at 80 F., and 8.35 B.t.u.s per square foot per hour at F.

Experience has shown that during the construction of metallic receptacles 10, the metal becomes uneven in surface, especially Where stiffeners and other structural members are attached thereto by welding. Since the insulation blocks 16 must be firmly attached to the metal manually, such irregularities may cause air bubblesof varying sizes to Ibe entrained in the fast-curing adhesive used for attaching the blocks to the metal, especially when laying blocks on vertical or overhead surfaces. My research shows that blocks 16 with a facial dimension of up to 6 inches by 6 inches can be installed with adhesion of close to 100 percent of surface. Thereafter, the percentage of adhesion falls 01T rapidly, to a point where through imperfections in the adhesive, cryogenic fluid 12 may be vented from the fissures. In the present case, and for cryogenic uids 12 with an initial boiling point above 160 F., a maximum of 6 inches by 6 inches should be used.

Having determined in this case that insulating core 40 should be 7.500 inches thick to provide the desired rate of vaporization of confined liquefied gas 12, in blocks 16 with a facial dimension of 6 inches by 6 inches, blocks of fused volcanic glass are cut having cross-sectional dimensions of 5.950 inches Iand a length of 7.500 inches. The reduction of 50 mils less than the desired finished cross-sectional dimension is to provide space for the encapsulating material. At the same time, a small, centrally located perforation is drilled through the length of the block to permit the escape of air during the subsequent encapsulation. Metallic molds with inside crosssection measuring exactly 6 inches by 6 inches and a useful depth of more than 71/2 inches are fabricated to encapsulate the volcanic glass cores 40 within the outer protective sheathing 42 of polyurethane material, which molds are heated to about 240 F. before liquid polyurethane in measured quantity is injected therein. The volcanic glass block then is pressed into a central location within the mold, after which the mold containing the liquid polyurethane and the volcanic brick is oventreated at about 250 F. until it hardens, e.g., for about 30 to 60 minutes, to produce volcanic glass block 16 having a skin of the polyurethane material on all sides as well as in the central perforation. The freshly-encapsulated 4blocks 16 are allowed to cure for 48 to 72 hours, during which time and subsequently the water impermeable polyurethane shell 42 prevents any absorption of moisture by insulating core 40.

Similarly, when liquid meth-ane -at an initial boiling point of 259 F. is the intended cargo, insulating blocks 16 having interior faces 4.0 inches square, -are calculated from the product of the maximum temperature variation of the face and the shrinkage factor to produce a maximum 10-mil fissure between adjoining innermost faces 48 of insulating blocks 16. Each block 16 is cut 18 inches thick to ensure -a heat flow of 6.0 B.t.u.s per square foot per hour into the cryogenic cargo from outer metal at 60 F., 5.05 B.t.u.s per square foot per hour on metal at 20 F., 5.50 B.t.u.s per square foot per hour on met-al at 40 F., 6.55 B.t.u.s per square foot per hour on metal at 80 F., and 7.05 B.t.u.s per square foot per hour on metal at 100 F. metal temperature. In the same manner as for propane, the volcanic glass blocks 16 are undercut `by 50 mils in fabricating insulating cores 40 before the blocks are pressed into molds measuringY exactly 4 inches by 4 inches inside cross-section and a useful depth of more tha-n 18 inches, wherein the volcanic glass blocks 16 are encapsulated within lan outer protective sheathing 42 of polyurethane material. Thus, as cach innermost face 48 contracts due to the reduced temperature of cryogenic liquid 12, fissures not greater than l mils are produced between each of the innermost adjoining faces, which Ifissures `are sutiiciently small to convert any cryogenic liquid ow therein to a saturated vapor in case of failure or absence of inner synthetic lining 70. The dimensions of insulating blocks 16, as determined by the specific coefficients of expansion/contraction of the insulating material utilized and the initial boiling point of the liquefied cargo to produce fissures of maximum dimension of mils, can be similarly calculated for any desired liquefied gas cargo, e.g., butane, ammonia, propane, propylene, ethane, ethylene, methane, nitrogen, etc. The polyurethane sheathing 42 in solid form has an expansion/shrinkage factor of about 0.70 x 10-4 per inch per inch F. or about 10 times that of insulating core 40. Since blocks 16 are dimensioned facially to produce a fissure of 10 mils maximum, elongation v-aries by sizes. For example, if a 12 inch by 12 inch facial dimension were required to shrink to 11.990 inches by 11.990 inches, coating 42, if not retained nor elongated by the core, would shrink to 11.900 inches by 11.900 inches. In this case, coating 42 is elongated by 0.8 percent due to being held by core 40. If a 4-inch by 4-inch dimension is shrunk to 3.990 inches by 3.990 inches.. coating 42 is elongated by 2.3 percent, since otherwise it would shrink to 3.900 inches by 3.900 inches if not held by core 40. Such elongation is only la small fraction of its capacity; the core material, with a compressive load of over p.s.i. and a tensile load of 45/ 50 p.s.i. is not crushed or damaged by the tension of coating 42 and has proven practical of much greater elongation at 320 F Referring to the wall section depicted in FIGURE 4, insulating blocks 16 are secured to metal shell 14 by utilizing as an adhesive the same liquid polyurethane material as is used for encapsulation and which is applied as 'a bonding agent between metallic shell 14 and outermost face 46 of the blocks. There is neither horizontal nor vetrical lateral bonding between blocks 16, which blocks 16 lie in juxtaposition, one abutting the other, to produce continuous horizontal seams and staggered verti- -cal seams, as is the practice in brick laying.

During the course of raising the walls, a layer of sheet material 54, inert and impervious to cryogenic liquid 12, and of low shrinkage, is positioned at intervals in horizontal courses .to limit the ow of vapors which may enter the walls in the absence or failure of inner lining 70 and endeavor to creep up through the vertical and horizontal seams. In this manner, vapors are blocked by all layers below the level of the contacting fluid, and those vapors generated in fissures in the one course immediately above the highest covered layer are the only vapors which are not blocked and able to vent into the vapor space. Suitable materials include films of polyethylene terephthalate resin sold under the trade name Mylar, tetrafluoroethylene polymers sold under the trade name Teflon, and polyamide resins sold under the trade name nylon.

When blocks 16 shrink, as is portrayed in exaggerated form in FIGURE 5, the fissures between adjoining blocks 16 are uniform and usually less than 10 mils, as determined from the previously calculated shrinkage resulting from the thermal effect of cryogenic liquids 12 adjacent to or in contact with the blocks. Therefore, whenever liquid 12 may endeavor to flow into these crevices 50, it is immediately converted into a saturated vapor which functions as a better insulator and is retained in all crevices by the contacting liquid 12, with the exception of the one course of fissures immediately above the highest liquid-covered course. Taking the ultimate case of there being no inner lining 70 in an internally insulated receptacle 10, having an internal periphery of 400 feet, maximum length of unblocked seam is 800 feet (horizontal and vertical) and minimum 400 feet (horizontal only). As soon as a course becomes unblocked vapor pressure on the s-unface of cryogenic liquid 12 is nulliied and there remains only the hydrostatic pressure in the course. Since courses 'are designed to 6 inches maximum, if cryogenic liquid 12 were to weigh 100 pounds per cubic foot, the maximum hydrostatic pressure in each course would be 5.5 ounces per square inch and have a mean of 2.33 ounces. Assuming the triangular conguration with a base of 0.010 inch, the mean is 0.005 inch. Therefore, the maximum opening is 48 square inches, and the minimum opening is 24 square inches, or a mean of 36 square inches. Among cryogenic gases, ammonia, at 42.6 lbs/ft.3 at 28 F., is probably the most susceptible to expansion. My tests with propane indicate a flow rate of about 60 inches per minute. Using this same rate, maximum of 12/3 c.f.m., 5/6 c.f.m. minimum, or a mean of 1% c.f.m. of liquid would be involved. This, expressed in terms of ammonia gas, at 70 F. means 1600 c.f.m. maximum, 800 c.f.m. minimum and a mean of 1200 c.f.m. -In the case of propane, 525 c.f.m. maximum, 263 c.f.m. minimum or a mean of 395 c.f.m. gas at 70 F. would be generated. Expressed in terms of thermal energy, 60 lbs. per minute maximum, 30 lbs. per minute minimum, with a mean of 45 lbs. of propane per minute would require 162,000 B.t,u.s per hour. To re-cool this gas, would require 18 tons of refrigeration maximum, 9 tons minimum, and a mean of 131/2 tons. Simultaneously, such a tank would have about 50,000 square feet of thermal surface transmitting 293,000 B.t.u.s per hour at 60 F. metal temperature, requiring about 25 tons of refrigeration. These teachings obtained from my research point up the fact that failure or absence of inner lining 70 is not catastrophic.

When the cryogenic receptacles 10 of this invention are fabricated from metals which are likely to become embrittled if exposed to the temperature of the cargo and are located in a frigid climate or a confined area, e.g., abroad ship where dead air spaces are difiicult to heat, it is necessary to install heating coils 60 along the outer periphery of metallic shell 14 to prevent the formation of ice which would act as an insulator to block the flow of heat required to maintain metal shell temperature. Heating coils 60 may then be used in lieu of conventional stiffeners, and spaced apart at such distances that a circulating heat transfer fluid entering each heating coil at calculated velocity and suitable temperature emerges at a temperature slightly above the minimum temperature at which the metal is to be maintained. Without this inward ow of heat Ifrom metallic outer shell 14, the Vapor seal within fissures 50 might not be formed to block cryogenic fluid 12 from contacting metallic shell 14, thereby reducing the temperature of the shell to its critical level and causing embrittlement. It will thus be seen that suitable metals are recommended, so as to minimize (a) thermal requirements, which cause ebullition, and (b) the need either for the recooling of vapors or of venting to maintain low vapor pressures, which is the prime purpose of this invention.

Although this invention has been described utilizing a rectangular cryogenic receptacle having flat walls, it is understood that insulating blocks 16 can be installed along the inner face of a circular tank by radius cutting the bricks on opposite faces 46 and 48 before encapsulating `the blocks in specially designed molds.

The provision of a plurality of indentations at regular intervals on faces 46 and 48 has been found to relieve the contractional stresses on the face produced by the low temperature of cryogenic fiuids 12, and, when applying adhesive during installation, to hold the adhesive in position until brought into contact with the metal.

I claim:

1. A receptacle for the confinement of cryogenic fluids comprising a metallic outer shell, a plurality of insulating blocks completely lining the interior of said outer shell, said blocks lying in juxtaposition with adjoining faces abutting, one face of said blocks being secured to the interior of said outer shell with the remaining faces being freely variable independently of the adjoining insulating block, the transverse dimension of the interior face of said block being so dimensioned that the fissures formed intermediate said interior faces by the temperature differential imposed by said cryogenic fiuids are sufciently small to convert any seepage of cryogenic fiuids therein to a saturated vapor barrier.

2. A receptacle according to claim 1 wherein an inner 12 liner consisting of any suitable material is placed between the plurality of insulating blocks and interior portion of said receptacle wherein the cryogenic fluids are placed.

3. A receptacle according to claim 2 in which the material comprising the inner liner is synthetic rubber.

4. A receptacle according to claim 1 in which the interior faces of said block are in contact with the cryogenic fluids.

S. A receptacle according to claim 2 wherein one-way release valves are placed in the top and uppermost porlions of the side walls of the inner liner to allow gases to escape from between the inner liner and said insulating blocks when the pressure therein builds up.

6. A receptacle according to claim 1 in which the interior faces of said block are in contact with the cryogenic fluids.

7. A receptacle according to claim 1 wherein said fissures are not more than about 0.125 inch in width.

8. A receptacle according to claim 1 wherein said fissures are not more than about 0.02 inch in width.

9. A receptacle according to claim 1 wherein said insulating blocks are encapsulated within a sheathing of organic plastic material.

10. A receptacle according to claim 9 in which the organic plastic material is a polyurethane.

11. The receptacle of claim 1 in which the insulating block is of foamed volcanic glass.

12. A receptacle according to claim 1 wherein heating means are provided along the outer surface of said metallic shell.

13. A receptacle according to claim 1 wherein layers of sheet material impervious to the fluids are positioned within horizontal courses of said insulation blocks, whereby the layers of sheet material limit the ow of vapors.

14. A method of manufacturing a thin metallic shelled insulated container for the retention of cryogenic fluids comprising (a) fabricating a plurality of insulating blocks, said blocks having one face so dimensioned that the contraction produced in a transverse direction by the reduced temperature of said cryogenic fluids produces ssures intermediate the faces sufiiciently small to convert any seepage of cryogenic fluid therein to a saturated vapor barrier, and (b) securing the face of said blocks opposite said one face to the interior of said metallic shell, each block being in juxtaposition with and independent of each adjacent block so that said blocks are free to contract or expand upon a variation in temperature.

15. A method of manufacture according to claim 14 wherein an inner liner consisting of any suitable material is fabricated and hung within the chamber formed by the plurality of insulating blocks attached to the metallic shell.

References Cited UNITED STATES PATENTS 2,114,546 4/1938 Slayter 52--612 2,268,251 12/1941 Haux 52-612 2,629,698 2/1953 Sterling 220-9 2,937,780 5/1960 Beckwith 220-9 2,958,442 11/1960 Lorentzen 220-63 2,983,401 5/1961 VMurphy 220-9 2,994,452 8/1961 Morrison 220-9 3,039,418 6/1962 Versluis 220-9 3,055,532 9/1962 Morrison 220-9 3,178,490 4/1965 Petrino et al.

3,298,150 1/1967 Ahlquist 52-406 3,298,345 1/1967 Pratt 220-9 3,325,037 6/1967 Kohn et al. 220-9 THERON E. CONDON, Primary Examiner. I. R. GARRETT, Assistant Examn'er. 

